1. Field of the Invention
The present invention relates to a monolithic integrated sensor element comprising a field effect transistor which is sensitive to a physical quantity to be detected and a non-volatile memory.
2. Description of the Prior Art
It is known to realize a sensor element and a non-volatile memory by two separate components on a chip. In so doing, e.g. an MOS transistor can act as a sensor and a second MOS transistor can act as a non-volatile memory. Known non-volatile memories of this type are EPROMs, Flash EPROMs, EEPROMs, etc. EEPROMs are frequently used as non-volatile memories in view of their simple programming. An analog storage of information in a single EEPROM cell can increase the storage density and simplify the circuit technologies for analog signal processing when long-term storage is required.
Since in the above-mentioned sensor elements according to the prior art the actual sensor and the non- volatile memory are realized by two transistors, a large chip area is necessary for realizing a sensor element. In addition, due to local parameter variations resulting from the manufacturing process, adaptation problems occur between the two transistors forming a sensor element, whereby a change in the output signal is caused. Furthermore, a signal processing unit is required which processes the sensor signal and the memory contents.
U.S. Pat. No. 4,788,581 relates to an MOS dosimeter used for measuring a dose within a radiation field. The dosimeter comprises a semiconductor substrate, an insulating layer on the semiconductor substrate, the insulating layer being resistant to the radiation and provided with a floating gate. In addition, a metal contact is connected to a semiconductor substrate. The floating gate is used for accumulating a charge, the accumulated charge corresponding to the dose of radiation. The accumulated charge can be reset for using the dosimeter once more.
JP-A-07115182 relates to a photoelectric transducer with a storage function in the case of which a silicon substrate has a layer provided therein into which a source layer and a drain layer have been diffused. A floating gate is arranged on a tunnel oxide film and, in addition, a control gate consisting of polycrystalline silicon is deposited on the floating gate, an oxide film being arranged between these two gates. A photoelectric transducer is formed by the photoconductive layer and a transparent electrode.
Thus there is a need to provide a space-saving sensor element with an associated non-volatile memory, the sensor element avoiding also adaptation problems between the sensor cell and the memory cell caused by local parameter variations resulting from the manufacturing process.